South Australia's six-day "circuit-breaker" lockdown will be cut short, officials said Friday, blaming a pizza parlour worker who misled contact tracers about how he contracted the virus.

Premier Steven Marshall indicated a tough lockdown for the state's almost two million people would end late on Saturday, at least two days earlier than planned.

Marshall said a man who claimed he was a customer at a pizza parlour hotspot -- leading authorities to believe the strain was virulent enough to be transmitted via a takeaway box -- in fact worked there.

"One of the close contacts linked to the Woodville pizza bar deliberately misled our contact-tracing team," said Marshall. "Their story didn't add up. We pursued them. We now know that they lied."

Authorities in Adelaide had ordered schools, shops, pubs, factories to close and stay-at-home orders were issued for residents across South Australia state
Authorities in Adelaide had ordered schools, shops, pubs, factories to close and stay-at-home orders were issued for residents across South Australia state AFP / Brenton EDWARDS

It is unlikely the man will face charges, police said. "The Emergency Management Act requires people to provide information on request," said police commissioner Grant Stevens. "There is no penalty for failing to truthfully answer those questions."

Red-faced authorities stressed the costly lockdown had still been necessary -- and that pizza parlour customers should still come forward for testing.

On Wednesday, they ordered schools, shops, pubs, factories and even takeaway restaurants to close and stay-at-home orders were issued for residents across the state.

Since then, tens of thousands of tests have shown no new community transmission and the cluster totals only 25 cases, leading to accusations that authorities overreacted.

People in Adelaide and the rest of the state will be able to leave their homes immediately to exercise, and most other restrictions will be eased late on Saturday.